An empirical correlation-based model to predict solid-fluid phase equilibria and phase separation of the ternary system CH4-CO2-H2S

To cover the expected increased demand for natural gas, energy industry has to exploit sour gas reserves located around the world. However, acid gases have to be removed before the natural gas produced from these fields could be used. One of the novel concepts in this field is the utilization of solid phase formation of carbon dioxide and/or hydrogen sulfide. The main aim of this study is to develop an empirical correlation model based on Peng-Robinson equation of state (PR EoS), with fugacity expressions, that is able for the first time to describe the solid-fluid phase equilibria for the ternary system of CH4-CO2-H2S at pressures from 5 to 30 bar and over a wide range of temperature (130-200 K). The model was first tested on the binary systems of CH4-CO2, CO2-H2S and CH4-H2S with optimized interaction parameters. When proven to be successful, it was then expanded in a predictive manner to describe the ternary system of CH4-CO2-H2S. The model predictions for the solidification points of 5 different mixtures were within the acceptable error when compared to the experimental data available in the literature. A model based on equilibrium stage separation unit was used to study the separation of three different feed compositions of this ternary system. Overall, it was found that separation of CO2 in solid phase improves when increasing the operating pressure up to 20 bar, and decreases at higher temperatures. Similarly, the separation of H2S in either liquid or solid phase improves at higher pressures and lower temperatures. The recovery of CH4 was high over the entire ranges of operating conditions, expect at high pressure (30 Bar) at temperatures below 190 K. This work provides scientists and engineers with an accurate tool that may be used with confidence for predicting solid-fluid phase equilibria. Consequently, this model eliminates difficulties associated with the need for experiments on ternary system solid-fluid phase equilibria. 2021 The Author(s)The publication of this article was funded by the Qatar National Library .Scopus2-s2.0-8510917127

A review on the solid-liquid-vapor phase equilibria of acid gases in methane

In spite of the increasing levels of greenhouse gases in the atmosphere, and their impact on the environment, the demand for natural/biogas will increase significantly in the coming few decades. To cover this demand, the global energy industry is continuously exploiting sour gas reserves located around the world. Nonetheless, sour gas has to be sweetened before the practical utilization of natural or biogas. The cryogenic separation technologies have emerged as a new technology to separate carbon dioxide (CO2) and hydrogen sulfide (H2S gases) from natural/biogas. The cryogenic separation produces less harmful gases, and can be less expensive to operate and maintain in comparison to the conventional technologies. To design cryogenic separation equipment, vapor-liquid equilibrium (VLE), solid-liquid equilibrium (SLE), solid-vapor equilibrium (SVE), and solid-liquid-vapor equilibrium (SLVE) data for the corresponding binary systems (of CH4-CO2, CH4-H2S, and H2S-CO2) and ternary system (of CH4-H2S-CO2) are required. The main target of this article is to review the SLVE data for the acid gases (CO2 and H2S) in methane (CH4) as the main constituent of natural/biogas. It will address SLVE data for the binary systems of CH4-CO2, CH4-H2S and H2S-CO2 as well as the ternary system of CH4-H2S-CO2. It will not only address the available laboratory data, but it will also discuss, compare and evaluate the different models used to correlate/predict these data.Open Access funding provided by the Qatar National Library.Scopus2-s2.0-8513234129

Prediction of solid-liquid-vapor phase equilibria of noble gases in nitrogen

The primary objective of this study is to develop an empirical correlation model that is able to predict the solid-liquid-vapour phase equilibria (SLVE) for the ternary system of N2-Kr-Xe at pressures ranging from 1 to 45 bar and temperatures ranging from 80 to 180 K. The model was based on Peng-Robinson equation of state. To optimize the interaction parameters that are needed in the model, it was first used to correlate the experimental SLVE data found in the literature for the N2-Kr, and N2-Xe and Kr-Xe binary systems. When the corresponding interaction parameters were optimized, the model was then expanded to predict the SLVE and construct the phase envelope of the ternary system of N2 -Kr-Xe.Open Access funding provided by the Qatar National Library. Not applicable. Although the scientific literature has extensively covered the thermodynamics of air components and air separation; there are little studies that cover the solid-fluid phase equilibria of nitrogen-noble gas mixture systems for their separation, despite their importance and presence in several industries. In this study, and for the first time, we attempt to model the solid-liquid-vapor equilibria (SLVE) of the ternary system Kr-Xe-N2 and its binary constituent systems (Kr-Xe, Xe-N2, and Kr-N2) using an empirical-correlation based model. Additionally, a three-phase solid-liquid-vapor (SLV) separation unit is developed to study and describe the SLVE phase envelope of the ternary system Kr-Xe-N2. Developing this model successfully will provide a useful tool to predict the SLV phase equilibrium behavior for the ternary system Kr-Xe-N2 and evaluate the performances of the corresponding three-phase SLV separation equipment without the need to conduct expensive and time-costly experiments. Furthermore, the model could be further developed and extended to different systems and gases mixtures.Scopus2-s2.0-8512734661

Virtual mimic of lab experiment using the computer-based Aspen Plus® Sensitivity Analysis Tool to boost the attainment of experiment's learning outcomes and mitigate potential pandemic confinements

The computer-based Aspen Plus® Sensitivity Analysis Tool (APSAT) was used as a virtual environment to mimic a gas absorption lab experiment in the Unit Operations Lab within the curriculum for the Bachelor of Science in Chemical Engineering at Qatar University. A pool of 35 students enrolled in three lab sections was utilized. The approach was applied in three stages to foster the attainment of the learning outcomes of the experiment by testing and evaluating some parameters that cannot be examined using the physical lab equipment. Results show that the approach helped the students gain a profound understanding and address conceptual mistakes while discussing the results of the APSAT outputs. Students who were engaged in the APSAT activity demonstrated a strong interest in this approach. This approach can be implemented to facilitate the teaching of lab courses. Furthermore, it is a practical choice to optimize the resources and a good substitute for lab experiments in case of any pandemic, confinement or interest in testing the effects of hazardous conditions to ensure sustaining the learning outcomes from corresponding experiments.The Qatar National Library and Qatar University funded the publication of this article. Funding Open access funding is provided by the Qatar National Library.Scopus2-s2.0-8514162046

Influence of carbon uniformity on its characteristics and adsorption capacities of CO2 and CH4 gases

Activated carbons of resorcinol-formaldehyde aerogels (AC-RFA) were prepared and mixed with multiwall carbon nanotubes (MWCNTs) with various ratios. Samples were characterized by different techniques. The novelty of the study is in evaluating the effect of uniformity of carbon nanocomposites on their performance for the adsorption of CH4 and CO2 gases as well predicting the separation of their mixtures. The results indicated that, by increasing the percentage of MWCNTs into the sample, its structural uniformity and order ascend. The capacities of CH4 and CO2 by adsorption were measured at various temperatures, and were correlated with the extended dual site Langmuir (DSL) model. Overall, results showed that the adsorption capacity of MWCNTs towards gases is relatively very low compared to that of activated carbons. The DSL model was utilized to forecast the separation of the binary CO2/CH4 mixed gas based on knowledge of single component adsorption isotherm parameters. Adsorption equilibrium data of the CO2/CH4 binary gas mixture was forecasted at different temperatures by DSL model in accordance with the perfect-negative (PN) or perfect-positive (PP) behaviors on the heterogeneous surface of the adsorbent.Acknowledgments: This publication was made possible by the NPRP award (NPRP 08-014-2-003) from the Qatar National Research Fund (a member of Qatar Foundation). Statements made herein are the sole responsibility of the authors. Technical support from the Department of Chemical Engineering, Central Laboratory Unit (CLU) and Gas Processing Centre (GPC) at Qatar University is also acknowledged. Further, the publication of this article was funded by the Qatar National Library.Scopus2-s2.0-8509922365

Adsorption of Carbon Dioxide, Methane, and Nitrogen Gases onto ZIF Compounds with Zinc, Cobalt, and Zinc/Cobalt Metal Centers

ZIF-8, Co-ZIF-8, and Zn/Co-ZIF-8 are utilized in adsorbing nitrogen (N2), methane (CH4), and carbon dioxide (CO2) gases at temperatures between 25 and 55 C and pressures up to 1 MPa. Equilibrium adsorption isotherms and adsorption kinetics are studied. The dual-site Langmuir equation is employed to correlate the nonisothermal adsorption equilibrium behavior. Generally, N2 showed the lowest equilibrium adsorption quantity on the three samples, whereas CO2 showed the highest equilibrium adsorption capacity. Amid the ZIF samples, the biggest adsorption quantities of N2 and CH4 were onto Zn/Co-ZIF-8, whereas the highest adsorption quantity of CO2 was on ZIF-8. The isosteric heats of adsorbing these gases on ZIF-8, Co-ZIF-8, and Zn/Co-ZIF-8 were examined. Moreover, the overall mass transfer coefficients of adsorption at different temperatures were investigated.Scopu

Natural Gas Sweetening Using an Energy-Efficient, State-of-the-Art, Solid-Vapor Separation Process

With the anticipated rise in global demand for natural gas (NG) and liquefied natural gas (LNG), sour gas reserves are attracting the attention of the gas industry as a potential resource. However, to monetize these reserves, sour natural gas has to be sweetened by removing acid gases (carbon dioxide and/or hydrogen sulfide) before liquefaction. The solidification of these acid gases could be the basis for their separation from natural gas. In this study, a state-of-the art solid-vapor (SV) separation unit is developed for removal of acid gases from methane and simulated using a customized Aspen Plus operation unit. The operating principles and conditions, mathematical model, and performance results are presented for the SV unit. Further performance analyses, means of optimization and comparisons to conventional methods used by the industry were studied. Results showed that for similar sweet gas purity, the developed SV unit consumes only 27% of the energy required by the amine sweetening unit. Furthermore, it saves on capital costs, as it requires less equipment and does not suffer from high levels of corrosion.Scopus2-s2.0-8513643009

Adsorption energy and pore-size distributions of activated carbons calculated using Hill's model

An integral equation derived using a statistical physics treatment by considering the adsorption energy distribution (AED) was used to model the adsorption of ethylene and ethane on resorcinol-formaldehyde-based activated carbon xerogels. Hill's model was taken as a local adsorption isotherm. This model was based on a grand canonical ensemble. Then a relationship between the energetic and the structural heterogeneities is used to determine the pore-size distribution (PSD) function. The AED and PSD obtained illustrate the greater affinity of activated carbon for adsorption of ethylene compared to ethane. In addition, this method was applied to determine the PSD of the British Drug House (BDH) activated carbon. The behaviour of the obtained PSDs at different temperatures was examined and related to the adsorption capacity of BDH activated carbon towards ethane, methane and nitrogen.Scopus2-s2.0-8492834888

Instability in CH3NH3PbI3 perovskite solar cells due to elemental migration and chemical composition changes

Organic-inorganic halide perovskites have rapidly grown as favorable materials for photovoltaic applications, but accomplishing long-term stability is still a major research problem. This work demonstrates a new insight on instability and degradation factors in CH3NH3PbI3 perovskite solar cells aging with time in open air. X-ray photoelectron spectroscopy (XPS) has been used to investigate the compositional changes caused by device degradation over the period of 1000 hrs. XPS spectra confirm the migration of metallic ions from the bottom electrode (ITO) as a key factor causing the chemical composition change in the perovskite layer besides the diffusion of oxygen. XPS results are in good agreement with the crystallographic marks. Glow discharge optical emission spectrometry (GD-OES) has also been performed on the samples to correlate the XPS results. Based on the experimental results, fundamental features that account for the instability in the perovskite solar cell is discussed. - 2017 The Author(s).The authors are thankful to the Center for Advanced Materials (CAM), Qatar University for the laboratory support during the experimental work. The authors are also grateful to the Gas Processing Center (GPC), Qatar University for providing the XPS analysis facility. Thanks to HORIBA Scientific – Jocelyne Marciano, Sofia Gaiaschi and Patrick Chapon for the GD measurements and interpretation. This publication was also made possible by NPRP grant # 6-175-2-070 from Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised